The present invention relates to an arrangement for the internal high-pressure forming of hollow profiles, and more particularly, to an arrangement for the internal high-pressure forming of a hollow profile, comprising an internal high-pressure forming tool, having a die sink into which the hollow profile is insertable, at least one axial die having a sealing head configured to be insertable with play into the hollow profile, which sealing head has a support part provided with a pressure fluid duct, on which support part a sealing arrangement is operatively held and which is rigidly connected with the axial die, and has a stop surface which rests in the operative position of the sealing head on the face side on the end of the hollow profile. The sealing arrangement contains at least one sealing element configured to be radially spread open for full sealing contact on an interior side of the hollow profile.
DE 43 09 680 A1 shows an arrangement in which a sealing head of an axial die is introduced in the hollow profile to be sealed and placed in the die sinking of an internal high pressure forming tool, until a radial shoulder of the sealing head stops on the face of the hollow profile. On its conically constructed end, the sealing head carries two sealing rings which are secured in the inserting direction against a sliding-out by a baffle plate mounted on the face of the end. The sealing ring close to the baffle plate is an O-ring made of a soft rubber-elastic material, while the sealing ring away from the baffle plate consists of polyamide and has a trapezoidal profile cross-section. The baffle plate is axially movably screwed to the face of the sealing head and has a bent edge, by way of which the O-ring can be acted upon. The sealing rings are constructed such that they can be introduced with a small play with respect to the hollow profile via the sealing head in a hindrance-free manner.
After the filling of the hollow profile in the known arrangement with the pressure fluid by way of the pressure fluid duct constructed in the sealing head, the sealing takes place on the basis of the internal high pressure which presses the baffle plate against the O-ring which, because of the sliding-up on the contact surface on the sealing head end which expands conically toward the axial die, spreads open and as a result presses radially against the hollow profile. Under the effect of the internal high pressure, the polyamide ring must also slide up on the contact surface and is then clamped because of its wedge-type construction between the contact surface and the hollow profile. Because of the thus occurring contact pressure on the hollow profile, an additional sealing of the hollow profile results. Furthermore, in this position, the polyamide ring represents a stop for the O-ring toward the axial die, thus against the inserting direction, whereby, by way of the axial contact pressure onto the polyamide ring by means of the internal-high-pressure-operated baffle plate, the O-ring deforms elastically and is further radially driven apart.
The arrangement advantageously avoids the previously customary metallic sealing which results in a plastic widening of the hollow profile and thus absolutely requires a trimming of the hollow profile which is formed to a finished state subsequently to the sealing. However, as long as no internal high pressure has built up during the filling operation, the sealing effect disadvantageously does not yet occur. This results in leakage because pressure fluid can flow off by way of the gap forming the play of the sealing rings. Furthermore, in practice, a sealing effect may or may not be achieved because the filling volume and the filling speed must be extremely high so that the baffle plate will move. Otherwise, a pressure compensation of the pressures occurs in front of and behind the baffle plate and thus there is no sealing of the hollowing profile during the internal high pressure forming. Thereby, because of the pressure drop during the process, the forming operation is not reliable. However, technically, the implementation of the indicated high filling speed or of the high filling volume is not feasible, particularly not in the case of relatively large components, such as motor vehicle axles.